JP5180065B2 - On-demand reverse link pilot transmission - Google Patents

Description

  The present disclosure relates generally to communication, and more specifically to pilot transmission in a communication system.

  In a communication system, when a base station processes traffic data, one or more modulated signals are generated, which are subsequently transmitted to one or more terminals on the forward link (FL). Sent. The forward link (or downlink) means a communication link from the base station to the terminal, and the reverse link (or uplink) means a communication link from the terminal to the base station. The base station can accommodate multiple terminals and can select a subset of these terminals for data transmission on the forward link at any given time.

  Typically, the base station improves the performance of FL data transmission by employing advanced scheduling and / or transmission techniques. For example, the base station can schedule terminals in a manner that accounts for frequency selective fading (or non-flat frequency response) observed by the terminals. In another example, the base station can perform beam shaping to direct FL data transmission to scheduled terminals. In order to employ advanced scheduling and / or transmission techniques, a base station typically needs to have a reasonably accurate estimate of the forward link channel response between the base station and the terminal.

  In the frequency division duplex (FDD) scheme, different frequency bands are assigned to the forward link and the reverse link. This may cause the forward link channel response not to correlate well with the reverse link channel response. In this case, the terminal needs to estimate its forward link channel response and send this forward link channel response back to the base station. As a result, the amount of signaling that needs to be sent back to the forward link channel estimation is typically prohibitive, which limits or prevents the use of advanced technology for FDD systems.

  In the time division duplex (TDD) method, the forward link and the reverse link share the same frequency band. One part of the time is assigned to the forward link and the other time part is assigned to the reverse link. In a TDD system, it is also assumed that a high degree of correlation between the forward link channel response and the reverse link channel response is possible, and that a reciprocity is possible. For reciprocal channels, the base station estimates the terminal's reverse link channel response based on the pilot transmitted by the terminal, and then estimates the terminal's forward link channel response based on the reverse link channel estimation can do. This simplifies channel estimation for the forward link.

  As described above, the base station can support a large number of terminals. Always requiring pilot transmission from all terminals leads to very inefficient utilization of system resources. This inefficiency appears as higher interference to other base stations and large overhead for pilots on the reverse link.

  Therefore, there is a need for a technique that can more efficiently transmit pilots in a communication system.

[Overview]
This document describes a technique for on-demand transmission of pilots on the reverse link, which is used to schedule terminals and process data for transmission on the forward link. It uses channel estimates derived from demand-type pilots. According to embodiments of the technology, the base station selects at least one terminal for transmitting on-demand pilots on the reverse link. Each selected terminal is a candidate for receiving data transmission on the forward link. This base station assigns a time / frequency assignment to each selected terminal. This time / frequency assignment may be a wideband pilot, a narrowband pilot, or any other type of pilot that is transmitted on the reverse link in addition to any pilot that the terminal needs to transmit. It may be. The base station receives and processes this pilot transmission from each selected terminal, and then derives a channel estimate for the terminal based on the received pilot transmission. The base station can schedule terminals for data transmission on the forward link based on the channel estimates of all terminals. The base station can further process the data for transmission to these terminals based on the scheduled channel estimates for each terminal. For example, the base station may use channel estimation and can perform beam shaping or eigensteering as described below.

  In the following, various aspects and embodiments of the invention will be described in more detail.

[Detailed description]
The term “exemplary” is used herein to mean “serving as an example, case, or illustration”. Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

  The on-demand pilot transmission technique described herein is used in various communication systems. Such communication systems include frequency division multiplexing (FDM) systems that transmit data to different frequency subbands, code division multiplexing (CDM) systems that transmit data using different orthogonal codes, and data transmission in different time slots. And a time division multiplexing (TDM) method. The Orthogonal Frequency Division Multiplexing (OFDM) scheme is an FDM scheme that efficiently partitions the overall bandwidth of the system into multiple (K) orthogonal frequency subbands. These subbands are also called tones, subcarriers, bins, frequency channels, etc. Each subband is associated with a respective subcarrier that is modulated with data. The Orthogonal Frequency Division Multiple Access (OFDMA) scheme is a multiple access scheme that utilizes OFDM.

  On-demand pilot transmission techniques can also be used for single-input single-output (SISO) systems, multi-input single-output (MISO) systems, single-input multi-output (SIMO) systems, and multi-input multi-output (MIMO) systems. Single input and multiple input are respectively associated with one antenna and multiple antennas of the transmitter. Single output and multiple output are associated with one and multiple antennas of the receiver, respectively.

  For the sake of clarity, most of the following description is devoted to the description of a TDD system with conflicting forward and reverse links. Further, this description assumes that each base station is equipped with multiple antennas, which are multi-input for forward link (FL) transmission and multi-output for reverse link (RL) transmission. Multiple antennas can also be used for advanced transmission techniques such as beamforming and eigensteering described below. For simplicity, the description relating to OFDM assumes that all K total subbands are not available for data and pilot transmission (ie, there are no guard subbands).

  FIG. 1 shows a TDD communication system 100 provided with a base station 110 that communicates with a wireless terminal 120. A base station may be a fixed station used for communication with a terminal, and is also called an access point, a Node B, or another terminology. Typically, the terminals 120 are desirably provided in the entire system, and each terminal may be fixed or mobile. A terminal is also called a mobile station, user equipment (UE), a wireless device, or some other terminology. Here, the terms “terminal” and “user” are used interchangeably. Each terminal can communicate with one or possibly multiple base stations on the forward and reverse links at any given time. In FIG. 1, a solid line with arrows at both ends represents data transmission on the current forward and / or reverse link, and a dashed line with arrows at both ends represents a potential data transmission in the future. Centralized construction, the system controller 130 provides matching and control to the base station 110.

  FIG. 2 shows a process 200 performed by a base station to perform data transmission on the forward link in the form of on-demand pilot transmission on the reverse link. Initially, the base station selects a set of one or more terminals for on-demand pilot transmission on the reverse link (block 210). A base station can accommodate multiple terminals on the forward link at any given time, but can only transmit data to one subset of these terminals. A terminal selected for on-demand pilot transmission on the reverse link is currently scheduled to be used for FL data transmission in a subsequent time interval, terminal receiving FL data transmission from the base station It may be a terminal, a terminal that receives future FL data transmissions, or a combination thereof. An on-demand pilot is added to any pilot required for the terminal to transmit.

  The base station assigns to each selected terminal a time / frequency assignment for on-demand pilot transmission on the reverse link (block 212). This time / frequency assignment for each selected terminal is a well-defined time interval and / or well-defined frequency subband that transmits an on-demand pilot, which may be a wideband pilot, a narrowband pilot or another type of pilot. Represents. The time / frequency allocation for each selected terminal depends on various factors such as, for example, the channel structure used by the forward and reverse link systems, the transmission mode of the on-demand pilot, the intended use of the on-demand pilot You may depend on The specified time / frequency assignment is sent to the selected terminal by an explicit and / or implicit signal (block 214). For example, a terminal that is currently receiving FL data transmissions can transmit on-demand pilots on the reverse link without explicit signaling. On the other hand, a terminal that is or can be scheduled to perform FL data transmission can receive an explicit signal that represents a specified time / frequency assignment.

  The base station receives and processes on-demand pilot transmissions on the reverse link from all selected terminals (block 216). The base station derives an RL channel estimate for each selected terminal based on the pilot received from the terminal (block 218). In a TDD system, it can be assumed that the forward and reverse links are reciprocal. This allows the base station to derive an FL channel estimate for each selected terminal based on its RL channel estimate (block 218). By performing on-demand pilot transmission, a base station can be scheduled or transmitted to transmit FL data without incurring a large overhead or consuming a large amount of reverse link resources. In addition, the latest forward link channel information can be acquired.

  The base station can employ advanced scheduling and / or transmission techniques to improve the performance of FL data transmission. The base station may schedule terminals to transmit FL data based on the FL channel estimates of all terminals selected to perform on-demand pilot transmission on the reverse link (block 220). The base station, for example, (1) performs multi-user diversity scheduling, selects a terminal with excellent FL channel estimation for FL data transmission, (2) performs frequency-sensitive scheduling, and has excellent FL Select a terminal for transmitting FL data on a subband with channel gain and / or perform another type of channel dependent scheduling. The base station may further transmit data to the scheduled terminal based on these FL channel estimates (block 222). The base station can perform beam shaping, for example, towards a terminal that is scheduled to transmit FL data. Further, the base station can perform eigensteering to transmit multiple data streams to the scheduled terminal. In the following, beam forming, eigensteering and the various blocks in FIG. 2 will be described.

  FIG. 3 shows an exemplary frame structure 300 of the TDD system 100. Data transmission on the forward and reverse links occurs in units of TDD frames. Each TDD frame may span a fixed or variable time. Each TDD frame is further divided into (1) a forward link (FL) slot in which data and pilot are transmitted on the forward link, and (2) a reverse link (RL) slot in which data and pilot are transmitted on the reverse link. Partitioned. As shown in FIG. 3, the FL slot may precede the RL slot or vice versa. Each slot can have a fixed time or a variable time.

  The terminal can transmit on-demand pilots in various manners on the reverse link. The on-demand pilot may be a wideband pilot that allows the base station to employ advanced scheduling techniques as well as advanced transmission techniques. The on-demand pilot may also be a narrowband pilot that allows the base station to employ advanced transmission techniques on well-defined subbands. In the following, several embodiments of on-demand pilot transmission will be described.

  FIG. 4 shows an embodiment of on-demand pilot transmission on a segmented channel. In this embodiment, signal transmission on the reverse link is performed using the channel structure 400 provided with frequency hopping. The entire system bandwidth is divided into S frequency segments, where typically S> 1. For example, the system bandwidth is 20 MHz and four segments can be formed as shown in FIG. 4, each of which may be 5 MHz. S signaling channels with S segments are formed. During each hop, each signaling channel is mapped onto one segment and hops from segment to segment over time to achieve frequency diversity. The hop period may span one TDD frame (as shown in FIG. 4) or multiple TDD frames. Hopping may be based on a frequency hopping (FH) function / sequence f (s, n) that selects a distinct segment s for each hop period n.

  Each terminal is designated with one signaling channel for signal transmission on the reverse link. This signaling may include, for example, a channel quality indicator (CQI), acknowledgment of a packet received on the forward link (ACK), and the like. A signal transmission channel for one terminal is indicated by a box with a cross pattern in FIG.

Each terminal also transmits a regular pilot on the designated signaling channel. A regular pilot is a pilot that the terminal needs to transmit. The terminal can perform regular pilot transmission and signaling separately (eg, using TDM, FDM, CDM), or can incorporate pilots into signaling. For example, the terminal can transmit an N-bit signal transmission value as follows. (1) Identify the code sequence associated with this signaling value from 2 ^N possible code sequences, (2) generate a waveform in this code sequence, and (3) transmit this waveform. The base station receives this transmitted waveform, determines a code sequence hypothesized to be most likely transmitted based on the received waveform, removes this hypothesized code sequence from the received waveform, and removes it Subsequent waveforms are processed to estimate RL channel response.

  The base station can obtain an RL channel estimate for the terminal based on regular pilots sent on the signaling channel specified for this terminal. The base station can transmit data to the terminal on all or part of the segment used by the designated signaling channel. In this case, the base station can use RL channel estimation for the signaling channel designated to transmit FL data to the terminal. The base station can also transmit data to the terminal on one or more segments that are not used by the designated signaling channel. In this case, the base station can instruct the terminal to transmit on-demand pilots on the segment (s) it uses. In the case of the example shown in FIG. 4, the terminal is segmented on segment 2 during hop period n + 2, segment 3 during hop period n + 3, segment 2 and 4 during hop period n + 4, and segment during hop period n + 5. 2 on-demand pilots are transmitted.

  FIG. 4 shows an example of transmitting an on-demand pilot on one or more additional segments located near a segment used by a designated signaling channel. In general, on-demand pilots can be sent on any number of segments and on any segment. On-demand pilot transmission can reduce RL overhead while providing the base station with the feedback necessary to efficiently transmit data on the forward link.

  FIG. 5 shows an embodiment of broadband on-demand pilot transmission for channel structure 500. For this embodiment, each terminal transmits data along with regular pilots on the reverse link at times scheduled for RL data transmission, and does not transmit pilots at unscheduled times. Each terminal transmits a broadband on-demand pilot on the reverse link at any time commanded by the base station. Multiple terminals can transmit wideband on-demand pilots simultaneously in one time window designed for on-demand pilot transmission. In this case, the window occurs (as shown in FIG. 5) within each TDD frame, within each scheduling interval, and so on. The broadband on-demand pilot may be generated in various ways. In order to mitigate pilot-to-pilot interference between multiple terminals, wideband on-demand pilots transmitted by the terminals can be orthogonalized in the frequency domain or time domain.

  In some embodiments, the terminal uses CDM to generate a broadband on-demand pilot in the frequency domain. This terminal covers the pilot symbols of each frequency subband together with the orthogonal code specified for this terminal. This orthogonal code may be a Walsh code, an orthogonal variable spreading factor (OVSF) code, a quasi-orthogonal function (QOF), or the like. Covering is a process of multiplying a transmitted symbol by all L chips of an L-chip orthogonal code to generate L covered symbols. Coated symbols are sent during L symbol periods. In an OFDM-based system, the terminal further generates an OFDM symbol for this symbol period by processing this covered symbol for all K subbands during each symbol period. The terminal transmits the broadband on-demand pilot with an integer that is a multiple of L symbol periods. Different orthogonal codes are specified for each terminal. The base station can recover the broadband on-demand pilot from each terminal based on the designated orthogonal code.

  In another embodiment, the terminal uses CDM to generate a broadband on-demand pilot in the time domain. In the case of this embodiment, the terminal generates L covered symbols by covering pilot symbols with L chip orthogonal codes assigned thereto. The terminal then spreads the L covered symbols across the entire system bandwidth (eg, all K subbands in an OFDM-based system) with a pseudo-random number (PN) code common to all terminals. Spread spectrum. The terminal transmits the broadband on-demand pilot in an integer that is a multiple of L sample periods. The base station can recover the broadband on-demand pilot from each terminal based on the designated orthogonal code.

  In yet another embodiment, the terminal generates a broadband on-demand pilot in the time domain with a PN code assigned to the terminal. For this embodiment, the terminal spreads the pilot symbols over the entire system bandwidth with a designated PN code used for both orthogonalization and spread spectrum. Each terminal is assigned to a different PN code, and this PN code is a time shift different from a normal PN code. The base station can restore the broadband on-demand pilot from each terminal based on the designated PN code.

  In yet another embodiment, the terminal uses FDM and generates a broadband on-demand pilot in the frequency domain. For example, M sets of subbands may be formed with a total of K subbands, with each set providing K / M subbands. Distributing the K / M subbands in each set over the entire system bandwidth (eg, uniformly) allows the base station to derive a channel estimate for the full system bandwidth. A set of M subbands can be assigned to M different terminals for on-demand pilot transmission. Each terminal can transmit a broadband on-demand pilot on a designated subband set. The base station can recover the broadband on-demand pilot from the designated set of subbands for each terminal. The base station can also derive channel estimates over the entire system bandwidth by performing interpolation, least squares approximation, etc. on the received wideband pilot.

  In the example shown in FIG. 5, the terminal transmits a broadband don-demand type pilot in TDD frames n + 2, n + 3, and n + 5. This allows the base station to obtain an estimate for the RL channel for this terminal over the entire system bandwidth based on the broadband on-demand pilot. The base station can transmit data to terminals on all or part of the system bandwidth using the FL channel channel designation derived from the RL channel estimation.

  FIG. 6 shows an embodiment of narrowband on-demand pilot transmission. In this embodiment, data transmission on the forward link is performed using a channel structure 600 with frequency hopping. A total of K subbands are arranged in G groups so that each group contains S subbands. In this case, generally G> 1, S ≧ 1, and G · S ≦ K. The subbands within each group may be continuous or non-contiguous (eg, distributed over a total of K subbands). G traffic channels may be formed of G subband groups. Each traffic channel is mapped to one subband group within each hop period and is hopped from subband group to subband group over time to achieve frequency diversity. The hop period may span one TDD frame (shown in FIG. 6) or multiple TDD frames. G frequency hopping FL traffic channels can be used for FL data transmission. FIG. 6 shows a subband group used for one FL traffic channel c. The channel structure for the reverse link may be the same as or different from the channel structure for the forward link.

  The base station can transmit data to a maximum of G terminals using G FL traffic channels. The base station selects terminals for on-demand pilot transmission, designates FL traffic channels for these terminals, and transmits a narrowband on-demand pilot on the reverse link on the designated FL traffic channel. Command the terminal. The selected terminal may or may not transmit data to the base station on the reverse link. The selected terminal can transmit its narrowband on-demand pilot within an appointed time window that occurs in each TDD frame (shown in FIG. 6), each hop period, each scheduling interval, and so on. In order to use the RL channel estimate obtained from the on-demand pilot for FL data transmission, the on-demand pilot transmission on each FL traffic channel precedes the FL data transmission on the same traffic channel. In the example shown in FIG. 6, the FL traffic channel c uses subband group 4 in hop period n + 1, subband group 5 in hop period n + 2, and subband group 2 in hop period n + 3. A terminal assigned FL traffic channel c for on-demand pilot transmission is narrow on subband group 4 in hop period n, on subband group 5 in hop period n + 1, and on subband group 2 in hop period n + 2. Send band on demand pilot. Multiple terminals may transmit narrowband on-demand pilots on the same traffic channel in the same data frame using CDM, TDM, and / or FDM.

  The base station obtains narrowband RL channel estimates for these terminals based on the narrowband on-demand pilot received from each selected terminal. The base station can use narrowband RL channel estimation (eg, for beam shaping) to perform FL data transmission to the terminal. The base station can also obtain a wideband channel estimate by collecting narrowband channel estimates over a period of time, which can be used for frequency sensitive scheduling.

  4-6 illustrate three exemplary on-demand pilot transmission schemes for the reverse link. The broadband on-demand pilot (for example, the one shown in FIG. 5) allows the base station to acquire more channel information about the forward link by consuming more resources on the reverse link. Narrowband on-demand pilots (eg, those shown in FIG. 6) allow the base station to obtain more channel information for only the subbands of interest, thereby minimizing the consumption of reverse link resources. Can do. A combination of a wideband on-demand pilot and a narrowband on-demand pilot can also be used. For example, terminals that can be scheduled for FL data transmission can transmit wideband on-demand pilots, while terminals that are already scheduled can transmit narrowband on-demand pilots. Various other on-demand pilot transmission schemes are possible and are encompassed within the scope of the present invention.

  In general, on-demand pilots can be transmitted in any part of the RL slot. In some embodiments, a portion of the RL slot (eg, several OFDM symbols) in each TDD frame is inverted for use as an on-demand pilot. This inverted part is placed towards the end of the RL slot to minimize the time between RL on-demand pilot transmission and FL data transmission using FL channel estimation derived from on-demand pilot. be able to. In another embodiment, the on-demand pilot is transmitted in the inverted portion of the entire P TDD frame. In this case, P may be an arbitrary integer. P can also be selected individually for each terminal. For example, it may be a small value of a mobile terminal provided with a channel condition that changes rapidly, or a large value of a stationary terminal provided with a relatively static channel condition. In yet another embodiment, an on-demand pilot is transmitted on top of another transmission on the reverse link. In this embodiment, on-demand pilots act as interference to other RL transmissions or vice versa. The on-demand pilot and other RL transmissions are then transmitted in a manner that causes this interference. On-demand pilots can be sent in other ways.

  On-demand pilot transmission may be used in systems that employ an incremental redundancy (IR) transmission scheme on the forward link. This scheme is also referred to as a hybrid automatic repeat request (H-ARQ) transmission scheme. The base station generates an encoded packet by encoding the data packet using H-ARQ, and further partitions the encoded packet into a plurality of encoded blocks. The first encoded block may contain sufficient information to cause the terminal to recover the data packet under excellent channel conditions. The other encoded blocks contain further redundant information about the data packet.

  The base station transmits the encoded blocks for the data packets to the terminal one at a time starting from the first encoded block. The first block transmission is also called a first H-ARQ transmission, and each subsequent block transmission is also called an H-ARQ retransmission. The terminal receives each transmitted encoded block, performs symbol reorganization for all received encoded blocks, decodes the reorganized symbols, and correctly decodes the packet Or whether it was decoded in error. If the packet is correctly decoded, the terminal sends an acknowledgment (ACK) to the base station, and the base station ends the packet transmission. Conversely, if a packet is decoded in error, the terminal sends a negative acknowledgment (NAK) and the base station sends the next encoded block (if any) to this packet. Send. Block transmission and decoding continues until the packet is correctly decoded by the terminal, or until all the encoded blocks for the packet are transmitted by the base station. Typically, ACKs are sent explicitly and NAKs are sent implicitly (eg, inferred by lack of ACK). Or vice versa. For clarity purposes, the following description assumes that ACK and NAK are sent explicitly.

  In the transmission of each block by H-ARQ transmission, some delay occurs to the terminal in order to decode the packet and send feedback (for example, ACK or NAK) of this packet. Some delay occurs in the base station to determine whether to transmit another encoded block. To clarify this delay, the transmission time line can be partitioned into multiple (Q) interlaces, in which case Q> 1 in general. For example, two jumps can be defined, such as jump 1 for a TDD frame with an even index and jump 2 for a TDD frame with an odd index. The base station can transmit one encoded block on the traffic channel in each TDD frame and transmit encoded blocks of Q different packets on Q interlaces.

  FIG. 7 shows an embodiment of H-ARQ transmission with on-demand pilot transmission in a TDD system with two interlaces. In the example shown in FIG. 7, the base station transmits the first encoded block of the new packet A to the terminal u on the interlace 1 in the TDD frame n. Terminal u receives this first encoded block, erroneously decodes packet A, and transmits a NAK in TDD frame n. The base station receives this NAK, decides that another coded block needs to be sent for packet A, and sends a request for on-demand pilot in TDD frame n + 1 to terminal u. Since both the base station and terminal u know that the next block transmission on jump 1 is for terminal u, this pilot request may be implicit and actually sent. It does not have to be done. The base station may transmit a block encoded for another packet to terminal u or another terminal on jump 2 in TDD frame n + 1. This is not clearly shown in FIG.

  Terminal u receives the pilot request and transmits an on-demand pilot on the reverse link in TDD frame n + 1. The base station receives this on-demand pilot from terminal u, derives an RL channel estimate for terminal u, processes the second encoded block for packet A using the RL channel estimate, and TDD frame n + 2 This block is transmitted to the terminal u on the jump 1 in FIG. Terminal u receives the second encoded block, correctly decodes packet A based on the received first and second decoded blocks, and sends an ACK in TDD frame n + 2. The base station receives ACK and determines that transmission of packet A can be completed.

  The base station transmits a new packet B to terminal u or another terminal on jump 1 starting from TDD frame n + 4. The base station selects one or more terminals (terminal u and / or another terminal) for on-demand pilot transmission and explicitly and / or implied the pilot request to each selected terminal in TDD frame n + 3. To send. Each selected terminal receives the pilot request and transmits an on-demand pilot on the reverse link in TDD frame n + 3. The base station receives and processes this on-demand pilot from all selected terminals and derives RL channel estimates for each terminal. By adopting advanced scheduling techniques, the base station can schedule terminals for FL data transmission based on the RL channel estimation of all selected terminals. The base station then sends the first encoded block for new packet B to the scheduled terminal (eg, using RL channel estimation) in jump 1 on TDD frame n + 4 . For this embodiment, the base station can obtain the RL channel estimate for the scheduled terminal prior to the first block transmission, and advanced scheduling and / or transmission techniques to transmit the first block. Can be used.

  The process shown in FIG. 7 is for one FL traffic channel. This same processing can be performed for each FL traffic channel supported by the base station.

  In the embodiment shown in FIG. 7, the base station transmits data in one jump a (eg, jump 1) and sends a pilot request in another jump b (eg, jump 2). The feedback (ACK or NAK) of the current packet transmission on interlace a determines which terminal should transmit the on-demand pilot on the reverse link. If another block transmission is required, the terminal that is currently receiving the packet transmission in jump a should continue to transmit the on-demand pilot. Alternatively, another terminal can be scheduled to transmit a new packet in jump a and transmit an on-demand pilot.

  The embodiment shown in FIG. 7 assumes that the terminal receives a block transmission on a given TDD frame, decodes the packet, and sends feedback in the same TDD frame. A delay of one TDD frame occurs at the base station to send a pilot request and at the terminal to send an on-demand pilot on the reverse link. If the decoding delay is longer than the interlace period and the terminal cannot send feedback in the same TDD frame, it will account for the additional delay incurred to support on-demand pilot transmission One or more additional jumps can be defined.

  FIG. 8 shows an embodiment of H-ARQ transmission with on-demand pilot transmission in a TDD system with three interlaces. In the example shown in FIG. 8, the base station transmits the first encoded block of packet A to terminal u in interlace 1 in TDD frame n. Terminal u receives the first encoded block, erroneously decodes packet A, and sends a NAK in TDD frame n + 1 to cause a decoding delay. The base station receives the NAK and sends a pilot request to terminal u in TDD frame n + 2. Terminal u receives the pilot request and transmits an on-demand pilot on the reverse link in TDD frame n + 2. The base station receives the on-demand pilot from terminal u, processes it, derives the RL channel estimate, and then on the interlace in TDD frame n + 3, the second encoded block of packet A Is transmitted to the terminal u.

  Terminal u receives the second encoded block, correctly decodes packet A, and sends an ACK in TDD frame n + 4 to cause a decoding delay. The base station receives the ACK, selects one or more terminals for on-demand pilot transmission, and sends a pilot request to each selected terminal in TDD frame n + 5. Each selected terminal receives the pilot request and transmits an on-demand pilot on the reverse link in TDD frame n + 5. The base station receives and processes this on-demand pilot from all selected terminals, schedules the terminal for FL data transmission, and sends packet B to the scheduled terminal on interlace 1 in TDD frame n + 6. The first encoded block of is transmitted.

  In general, any number of interlaces can be defined to account for the retransmission latency for H-ARQ. As shown in FIG. 7, the interlace period is set long enough so that the terminal can quickly approve the block transmission. However, if the interlace period is longer than the coherent time of the communication link, the FL channel estimation obtained from the on-demand pilot may become out of date while the FL data transmission continues. . Providing a large number of interlaces in a short period may cause decoding delays and may reduce the time between RL on-demand pilot transmission and successive FL data transmissions.

  In the embodiment shown in FIG. 7 and FIG. 8, one delayed TDD frame is generated to support on-demand pilot transmission of H-ARQ transmission. This additional delay allows the base station to select one or more terminals for on-demand pilot transmission on the reverse link within each TDD frame. However, this additional delay may increase the H-ARQ retransmission latency, for example, as shown in FIG. This additional delay can be avoided by sending a theoretical pilot request.

  FIG. 9 shows an embodiment of H-ARQ transmission with theoretical on-demand pilot transmission in a TDD system with two interlaces. In the example shown in FIG. 9, the base station transmits the first encoded block for packet A to terminal u in interlace 1 in TDD frame n. Terminal u receives the first encoded block, erroneously decodes packet A, and sends a NAK in TDD frame n + 1.

  During the FL slot in TDD frame n + 1, the base station selects (or speculates) one or more terminals that will not receive a NAK from terminal u and will be able to receive block transmissions on jump 1 in TDD frame n + 2. To do. For example, the base station may have terminal u (currently receiving a packet transmission in jump 1) and one or more other terminals that may receive a block transmission in TDD frame n + 2. From this, an on-demand pilot can be requested. The number of terminals to select and which terminal to select depends on various factors such as the latest packet transmission trend to the terminated terminal u and the amount of reverse link resources available for on-demand pilot transmission. . The base station sends a pilot request to all selected terminals in TDD frame n + 1. Each selected terminal transmits an on-demand pilot on the reverse link in TDD frame n + 1.

  The base station receives the NAK from the terminal u in the TDD frame n + 1. The base station further receives and processes the on-demand pilot from terminal u from TDD frame n + 1 (assuming that terminal u is selected for on-demand pilot transmission), and performs RL channel estimation for terminal u. Derived and transmits the second encoded block of packet A to terminal u on interlace 1 in TDD frame n + 2. Terminal u receives this second encoded block, encodes packet A correctly, and sends an ACK in TDD frame n + 3.

  The base station selects one or more terminals that will not receive an ACK from terminal u during the FL slot in TDD frame n + 3 and will be able to receive a block transmission on jump 1 in TDD frame n + 4. The base station sends a pilot request to the selected terminal in TDD frame n + 3. The base station receives ACK from the terminal u in the TDD frame n + 3, and ends the packet transmission of the terminal u. The base station then schedules terminal u or another terminal to perform a new packet transmission on jump 1 starting in TDD frame n + 4. If the scheduled terminal is selected for on-demand pilot transmission in TDD frame n + 3, the base station may estimate the FL channel based on the on-demand pilot received from the terminal in TDD frame n + 3. And then, in TDD frame n + 4, FL channel estimation can be used for FL data transmission. If the scheduled terminal is not a terminal selected for on-demand pilot transmission in TDD frame n + 3, the base station does not use advanced transmission techniques for the first block transmission to the terminal. The base station can use advanced transmission techniques for subsequent block transmissions to this terminal.

  As shown in FIG. 9, the theoretical pilot request does not introduce additional delay to support on-demand pilot transmission (and this does not cause retransmission latency). The base station can select two or more terminals for on-demand pilot transmission on the reverse link that has spent additional resources.

  In another embodiment of on-demand pilot transmission, a terminal scheduled for data transmission on the forward link transmits on-demand pilot on the reverse link for the entire period scheduled for this terminal. I do. In this embodiment, at the start of the scheduled interval, the base station does not have the terminal's FL channel estimate and transmits data to the terminal without knowledge of the FL channel response in the first transmission. Scheduled terminals receive an inherent request to transmit on-demand pilots on the reverse link. The base station can derive a terminal's FL channel estimate based on on-demand pilots and can employ advanced transmission techniques for each transmission to subsequent terminals. This embodiment has several advantages: (1) Efficient use of reverse link resources, (2) No additional delay to support on-demand pilot transmission, and therefore short retransmission latency, (3) Pilot request There is minimal or no signaling required to send.

  FIG. 10 shows an embodiment of a base station 110 and two terminals 120x and 120y in the TDD system 100. The base station 110 is equipped with a plurality (T) of antennas 1028a to 1208t, the terminal 120x is equipped with one antenna 1052x, and the terminal 120y is equipped with a plurality (R) of antennas 1052a to 1052r.

  On the forward link, at base station 110, data / pilot processor 1020 receives traffic data for all scheduled terminals from data source 1012 and sends signaling (eg, pilot request) from controller 1030. Receive. Data / pilot processor 1020 encodes, interlaces, and symbol maps traffic data and signaling to generate data symbols on the forward link and further generate pilot symbols. The data symbol used here is a modulation symbol for traffic / packet data, and a pilot symbol is a symbol for pilot (both transmitter and receiver know a priori). Modulation symbol is a complex value for one point in a signal point constellation for a modulation scheme (eg, M-PSK or M-QAM), and the symbol is an arbitrary complex value. TX spatial processor 1022 performs spatial processing on the data symbols of the advanced transmission technique, multiplexes within the pilot symbols, and provides transmit symbols to transmitter units (TMTR) 1026a-1026t. Each transmitter unit 1026 processes its transmission symbols (eg, those of OFDM) to generate a FL modulated signal. FL modulated signals from transmitter units 1026a-1026t are transmitted to each of antennas 1028a-1028t.

  At each terminal 120, one or more antennas 1052 receive the transmitted FL modulated signals and provide the signals received by each antenna to a corresponding receiver unit (RCVR) 1054. Each receiver unit 1054 performs processing to supplement the processing performed by the transmitter unit 1026 and provides received symbols. In the case of multi-antenna type terminal 120y, reception (RX) spatial processor 1060y performs spatial processing on the received symbols to detect symbols. This is an estimate of the transmitted data symbols. For each terminal, symbol demapping, inverse crossing, and decoding of the symbol received or detected by the RX data processor 1070 are performed, and the decoded data is provided to the data sink 1072. RX data processor 1070 also provides detected signaling (eg, pilot request) to controller 1080.

  On the reverse link, traffic data from data source 1088 and signaling (eg, ACK / NAK) sent by each terminal 120 is processed by data / pilot processor 1090, and further if multiple antennas are present Processed by TX spatial processor 1092, then coordinated by transmitter unit (s) 1054 and transmitted from antenna (s) 1052. In the base station 110, the RL modulated signal transmitted from the terminal 120 is received by the antenna 1028, adjusted by the receiver unit 1026, and then processed by the RX spatial processor 1040 and the RX data processor 1042 in the terminal. Processed in complementary style. RX data processor 1042 provides the decoded data to data sink 1044 and provides detected signaling to controller 1030.

  The control devices 1030, 1080x, and 1080y control the operation of the processing unit in each of the base station 110 and the terminals 120x and 120y. Memory units 1032, 1082 x, and 1082 y store data and program codes used by control devices 1030, 1080 x, and 1080 y, respectively. A scheduler 1034 schedules terminals for data transmission on the forward and reverse links.

  In the case of on-demand pilot transmission, control device 1030 can select a terminal that performs pilot transmission on the reverse link. At each selected terminal, data / pilot processor 1090 generates an on-demand pilot, and if present, TX spatial processor 1092 processes the pilot and then coordinates by transmitter unit (s) 1054 And transmitted from the antenna (s) 1052. At base station 110, on-demand pilot transmissions from all selected terminals are received by antenna 1028, processed by receiver unit 1026, and provided to channel estimator 1036. The channel estimator 1036 estimates the RL channel response for each selected terminal, determines FL channel estimates for these terminals based on the RL channel estimate for each selected terminal, and selects all the selected terminals. FL channel estimation is provided to controller 1030. The scheduler 1034 may schedule the terminal to transmit FL data by using FL channel estimation for advanced scheduling techniques (eg, frequency sensitive scheduling). Controller 1030 and / or TX spatial processor 1022 may transmit data to the scheduled terminal using FL channel estimation for advanced transmission techniques (eg, beamforming or eigensteering).

In FIG. 10, a MISO channel is formed between the base station 110 and the single antenna type terminal 120x. This MISO can be characterized by a 1 × T channel response row vector h _x (k) for each subband k and can be expressed as:

Where h _{x, j} (k), j = 1,. . . , T are complex channel gains between antenna j of base station 110 and single antenna of terminal 120x for subband k. Although not shown for simplicity purposes, the channel response is also a function of time.

The base station 110 can perform spatial processing as follows to perform beam forming for the terminal 120x.

Here, s _x (k) is a data symbol transmitted to terminal 120x on subband k, and x _x (k) is provided with T transmission symbols transmitted from T antennas of the base station. " ^H " symbolizes conjugate transpose. Beamforming guides FL data transmission to terminal 120x and improves performance. Equation (2) represents that FL channel estimation is required for beamforming to terminal 120x.

Terminal 120x obtains the received symbol for FL data transmission. This is represented by a character expression.

Where ｈ h _x (k) ‖ ² is the overall gain observed by data symbol s _x (k), r _x (k) is the symbol received for subband k at terminal 120x, and w _x (k) is noise in the terminal 120x. Terminal 120x need not be aware of the beam shape performed by base station 110 and can process received symbols as if the FL data transmission was transmitted from one antenna.

In FIG. 10, a MIMO channel is formed between the base station 110 and the multi-antenna terminal 120y. This MIMO is characterized by an R × T channel response matrix H _y (k) for each subband k. This can be expressed as:

Here, i = 1,. . . , R and j = 1,. . . , _{I, j} (k) for T, is the complex channel gain for subband k between antenna j of base station 110 and antenna i of terminal 120y. The channel response matrix H _y (k) is orthogonalized via singular value decomposition (SVD) as:

Where U _y (k) is the unitary matrix of the left eigenvector, V _y (k) is the unitary matrix of the right eigenvector, and Σ _y (k) is a diagonal matrix of singular values for subband k. . The diagonal element of Σ _y (x) is a singular value representing the channel gain for the S eigenmodes of H _y (k), and S ≦ min {T, R}. This eigenmode can be viewed as an orthogonal spatial channel. Base station 110 may transmit data on the eigenmode of H _y (k) using the right eigenvector (or column) in V _y (k).

Base station 110 transmits data on this best eigenmode of H _y (k), for example, by performing spatial processing with the eigenvector of the best eigenmode similar to the beamforming shown in equation (2). be able to. The base station 110 can also transmit data on multiple eigenmodes of H _y (k) by performing spatial processing for eigensteering as follows:

Here, s _y (k) is a vector provided with a maximum of S data symbols transmitted simultaneously to terminal 120 _y on subband k, and x _y (k) is T antennas of base station 110. Is a vector provided with T transmission symbols transmitted from the terminal to the terminal 120y. Equations (5) and (6) indicate that FL channel estimation is required to perform eigensteering to terminal 120y.

Terminal 120y obtains the received symbol for FL data transmission, which is expressed as:

Here, r _y (k) is a vector provided with R received symbols for subband k, and w _y (k) is a noise vector at terminal 120y.

Terminal 120y performs receiver spatial processing (or spatially matched filtering) and recovers the transmitted data symbols as follows:

Where M _y (k) is the spatial filter matrix for subband k,

Is the noise after detection. Terminal 120y may derive the spatial filter matrix M _y (k) using any one of the following equations:

It is.

  Equation (9) is for matched filtering techniques, Equation (10) is for zero forcing techniques, and Equation (11) is for minimum mean square error (MMSE) techniques.

When requested by the base station 110, the single antenna type terminal 120x transmits an on-demand type pilot on the reverse link. The base station 110 receives j = 1,. . . , Derive an estimate of h _{x, j} (k) for T.

Multi-antenna terminal 120y also transmits an on-demand pilot on the reverse link when requested by base station 110. Terminal 120y sends to base station 110 i = 1,. . . , R and j = 1,. . . In order to be able to derive an estimate of h _{y, i, j} (k) for T, on-demand pilots can be transmitted in various ways. In some embodiments, terminal 120y uses CDM to coat the pilot from each antenna with a different orthogonal code. R different orthogonal codes are used for the R antennas of terminal 120y. In another embodiment, terminal 120y uses FDM and transmits a pilot for each antenna on a different subset of subbands. A subset of R different subbands is used for the R antenna. In yet another embodiment, terminal 120y uses TDM and transmits a pilot for each antenna at different time intervals. Terminal 120y may also transmit R pilots from the R antennas using a combination of CDM, FDM, TDM. In any case, the base station 110 recovers the pilot from each terminal antenna based on the orthogonal code, subband subset, and / or time interval used for each terminal antenna.

The terminal 120y can have only one transmission chain and can transmit from one antenna, but can receive from multiple antennas. In this case, the terminal 120y can transmit an on-demand pilot from only one antenna. Base station 110 may derive a row of channel response matrices H _y (k) associated with antennas that terminal 120y uses to transmit on-demand pilots. Next, the base station 110 performs pseudo eigenbeam shaping to improve performance. The base station 110 performs (1) random values, (2) random values selected so that the columns of H _y (k) are orthogonal to each other, and (3) the Fourier matrix Row, (4) fill the remaining rows of H _y (k) with some other matrix element. The base station 110 can use H _y (k) for beam shaping as shown in Equation (2) and for eigensteering as shown in Equation (6). The base station 110 also performs the QR factorization on _H y (k), to obtain the unitary matrix Q _y (k) and the upper triangular matrix R _y (k). Next, the base station 110 transmits data using Q _y (k).

  In the above description, it is assumed that the forward link and the reverse link are reciprocal. The frequency response of the transmission chain and the reception chain at the base station may be different from the frequency response of the transmission chain and the reception chain at the terminal. Specifically, the frequency response of the transmission chain and the reception chain used for FL transmission may be different from the frequency response of the transmission chain and the reception chain used for RL transmission. In this case, calibration is performed to account for differences in frequency response so that the overall channel response observed by FL transmission is in conflict with the overall channel response observed by RL transmission.

  As described above, the on-demand pilot transmission technique can be used in various communication systems. These techniques can be advantageously used in OFDMA systems, frequency hopping OFDMA (FH-OFDMA) systems, and other systems that provide narrowband transmission on the reverse link. In such a system, regular narrowband pilots can be sent with RL data transmissions, for example using TDM. The base station can use this regular narrowband pilot for coherent demodulation of RL data transmission and time / frequency tracking of the reverse link. In order to support FL data transmission, the use of RL resources is very high because many or all terminals are required to transmit regular broadband pilots continuously or periodically on the reverse link. It becomes inefficient. Of course, FL channel estimation and data transmission can be facilitated by sending wideband and / or narrowband on-demand pilots on the reverse link if necessary and when needed.

  The on-demand pilot transmission technique described in this specification can be realized by various means. For example, these techniques can be realized in hardware, software, or a combination thereof. The processing units used to perform or support on-demand pilot transmission at the base station are one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processors (DSPDs), programmable In logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, other electronic units designed to perform the functions described herein, or combinations thereof Realized. The processing unit used to perform or support on-demand pilot transmission at the terminal is implemented in one or more ASICs, DSPs, etc.

  The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments. Accordingly, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

1 shows a TDD communication system. The process of transmitting data on the forward link while performing on-demand pilot transmission on the reverse link is shown. 2 illustrates an exemplary frame structure for a TDD system. Fig. 4 shows on-demand pilot transmission on a segmented channel. Fig. 2 illustrates broadband on-demand pilot transmission. 2 illustrates narrowband on-demand pilot transmission. Fig. 4 shows on-demand pilot transmission for H-ARQ with two interlaces. Fig. 4 shows on-demand pilot transmission for H-ARQ with 3 interlaces. A theoretical on-demand pilot transmission is shown. 1 shows a block diagram of a base station and two terminals.

Claims (34)

A controller operative to select a subset from a set of terminals served by the apparatus for performing on-demand pilot transmission on the reverse link, wherein the subset includes at least one terminal, wherein the at least one One device is a candidate for sending data,
Operate to process the on-demand pilot transmissions from each of the at least one terminal and to derive a channel estimate for each terminal based on the on-demand pilot transmissions from the terminals A channel estimation device for
A processor that operates to process the data to transmit to each of the one or more terminals scheduled to perform data transmission using the channel estimate for each of the one or more terminals. When,
A device comprising:   The apparatus of claim 1, wherein the controller is operative to assign a time / frequency assignment for performing the on-demand pilot transmission on the reverse link to each of the at least one terminal. .   Each of the at least one terminal is assigned a frequency segment for transmitting a signal on the reverse link and transmitting a regular pilot, and the channel estimation apparatus transmits a signal from each of the at least one terminal. The apparatus of claim 1, wherein the apparatus is operative to process the on-demand pilot transmission on at least one additional frequency segment selected.   The channel estimator is configured to process a broadband on-demand pilot transmission from each of the at least one terminal, and based on the broadband on-demand pilot transmission from each terminal, a broadband channel for each terminal The apparatus of claim 1, wherein the apparatus operates to derive an estimate.   The channel estimator is configured to process a narrowband on-demand pilot transmission from each of the at least one terminal, and for each terminal based on the narrowband on-demand pilot transmission from each terminal The apparatus of claim 1, wherein the apparatus is operative to derive a narrowband channel estimate.   The apparatus of claim 1, wherein the controller is operative to request each of the at least one terminal to transmit a broadband on-demand pilot or a narrowband on-demand pilot.   The channel estimation apparatus operates to receive the on-demand pilot transmission from each terminal scheduled to transmit data before each data is transmitted to each terminal. Equipment.   The apparatus of claim 1, wherein the controller is operative to select the terminals scheduled to perform the data transmission to perform the on-demand pilot transmission on the reverse link.   The controller is configured to receive feedback for prior data transmission and to select the at least one terminal for the on-demand pilot transmission on the reverse link based on the received feedback. The apparatus of claim 1, wherein the apparatus operates.   Scheduling the one or more terminals to perform the data transmission based on the channel estimate derived for the at least one terminal selected to perform the on-demand pilot transmission on the reverse link The apparatus of claim 1, further comprising a scheduler that operates as follows.   The channel estimator is operative to derive a broadband channel estimate for each of the at least one terminal, and the scheduler is configured to operate on the frequency subband determined by the broadband channel estimate of the at least one terminal. The apparatus of claim 10, wherein the apparatus is operative to schedule the one or more terminals to perform data transmission.   Further comprising a scheduler that operates to schedule to perform the data transmission, whereby from each terminal scheduled to perform data transmission during the data transmission to each of the terminals performed in succession, the The apparatus of claim 1, receiving an on-demand pilot transmission.   The processor uses the channel estimate for one of the one or more terminals to perform beam shaping for one of the one or more terminals scheduled to perform the data transmission. The apparatus of claim 1, wherein the apparatus operates to perform.   The processor performs eigensteering for one of the one or more terminals scheduled to perform the data transmission using the channel estimate for one of the one or more terminals. The apparatus of claim 1, wherein the apparatus operates to perform.   The processor includes a pseudo eigenbeam for one of the one or more terminals scheduled to perform the data transmission using the channel estimate for one of the one or more terminals. The apparatus of claim 1, wherein the apparatus is operative to perform formation. A method for transmitting a pilot in a communication system, comprising:
Selecting a subset from a set of terminals served by the same service equipment to perform on-demand pilot transmission on the reverse link, wherein the subset includes at least one terminal, wherein the at least one terminal is Candidates for sending data,
Processing the on-demand pilot transmission from each of the at least one terminal;
Deriving a channel estimate for each of the at least one terminal based on the on-demand pilot transmission from each terminal, and performing data transmission using the channel estimate for each terminal Transmitting data to each of the terminals scheduled to
A method comprising: Selecting the at least one terminal to perform the on-demand pilot transmission on the reverse link;
Receiving feedback on pre-submission of data;
Selecting the at least one terminal to perform the on-demand pilot transmission on the reverse link based on the received feedback;
The method of claim 16 comprising:   The method of claim 16, further comprising scheduling the terminal to perform the data transmission based on the channel estimate derived for the at least one terminal.   The method of claim 16, further comprising spatially processing the data transmission to each of the scheduled terminals based on the channel estimate for each of the scheduled terminals. A device in a communication system, comprising:
Means for selecting a subset from a set of terminals served by a service device to perform on-demand pilot transmission on a reverse link, wherein the subset includes at least one terminal, wherein the at least one terminal is data Candidates for sending,
Means for processing the on-demand pilot transmission from each of the at least one terminal;
Means for deriving a channel estimate for each of the at least one terminal based on the on-demand pilot transmission from the terminals, and using the channel estimate for the terminals to perform the data transmission Means for transmitting data to each said terminal scheduled for
An apparatus comprising: Means for selecting the at least one terminal to perform the on-demand pilot transmission on the reverse link;
Means for receiving feedback on pre-transmission of data; and means for selecting at least one terminal to perform the on-demand pilot transmission on the reverse link based on the received feedback;
21. The apparatus of claim 20, comprising:   21. The apparatus of claim 20, further comprising means for scheduling a terminal to perform the data transmission based on the channel estimate derived for the at least one terminal.   21. The apparatus of claim 20, further comprising means for spatially processing the data transmission to each of the scheduled terminals based on the channel estimate for each of the scheduled terminals. A terminal in a communication system,
A controller that operates to receive a request to perform on-demand pilot transmission on a reverse link and to determine a time / frequency assignment for the on-demand pilot transmission; A member of a subset selected by the service device from a set of terminals served by the service device to receive the request;
A processor operable to generate the on-demand pilot transmitted on the reverse link of the time / frequency assignment, wherein the on-demand pilot transmission performed on the reverse link performs a data transmission A terminal used for scheduling the terminal for the purpose, spatially processing data transmission to the terminal, or performing both scheduling and spatial processing.   The processor is operative to handle transmission signaling on a frequency segment designated for the terminal, and the controller is on at least one additional frequency segment not designated for the terminal. Operative to receive the request to make the on-demand pilot transmission, and the processor is further configured to generate the on-demand pilot to be transmitted on the at least one additional frequency segment. 25. A terminal as claimed in claim 24, in operation.   25. The terminal of claim 24, wherein the processor operates to generate a broadband on-demand pilot that is transmitted on the reverse link, and the data transmission on the reverse link is narrowband.   25. The processor of claim 24, wherein the processor is operative to generate a narrowband on-demand pilot that is transmitted on a frequency subband that is on the reverse link and that can be used to transmit the data to the terminal. The listed terminal.   25. The processor of claim 24, wherein the processor is operative to generate the on-demand pilot using time division multiplexing (TDM), frequency division multiplexing (FDM), code division multiplexing (CDM), or a combination thereof. The listed terminal.   The processor uses time division multiplexing (TDM), frequency division multiplexing (FDM), code division multiplexing (CDM), or a combination thereof to generate the on-demand pilot transmitted from multiple antennas. 25. The terminal of claim 24, wherein the terminal operates.   The controller determines whether the packet sent to the terminal has been correctly decoded, and if the packet has not been correctly decoded, the controller on-demand on the reverse link. 25. The terminal of claim 24, wherein the terminal is operative to receive implicitly the request to make a typed pilot transmission. A method for transmitting a pilot in a communication system, comprising:
Receiving a request to perform on-demand pilot transmission on the reverse link at the terminal;
Determining a time / frequency allocation for the on-demand pilot transmission;
Transmitting the on-demand pilot on the reverse link with the time / frequency assignment, wherein the on-demand pilot transmission on the reverse link schedules the terminal for data transmission; Used to spatially process data transmission to the terminal, or to perform both scheduling and spatial processing;
The terminal is a member of a subset selected by the service device from a set of terminals served by the service device to receive the request;
A method comprising:   Further comprising signaling on a frequency segment designated for the terminal, wherein the request is for transmitting the on-demand pilot on at least one additional frequency segment not designated for the terminal. 32. The method of claim 31, wherein: Transmitting the on-demand pilot on the reverse link comprises:
32. The method of claim 31, comprising transmitting a broadband on-demand pilot on the reverse link. Transmitting the on-demand pilot on the reverse link comprises:
32. The method of claim 31, comprising transmitting a narrowband on-demand pilot on a frequency subband that is on the reverse link and can be used to transmit data to the terminal.

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